Chemistry Reference
In-Depth Information
by a glycosidic linkage (i.e., an oxygen bond between the α-C1 on the glucosyl sub-
unit and β-C2 on the fructosyl subunit) and thus, the compound behaves as a nonre-
ducing sugar.
Sucrose is used as an example herein to determine the structure of a sugar. The
1
H-NMR spectrum taken in D
2
O indicates there are only CH-OH resonances. Further
2-D NMR analysis indicates the couplings and connectivity of the protons. The assign-
ments of the sucrose protons are shown in Figure 5.4.
Figure 5.5 shows the
13
C NMR of sucrose. There are two distinct carbon signals
in the region of 95 ppm and 105 ppm, resonance signals that are typical of anomeric
C-1 carbons. All the other carbons in the spectrum are assigned as HC-OH, thus
confirming the absence of any C-OMe, C-OAc, or CH
3
signals, and furthermore,
there are no double bond carbons in the molecule.
The molecular weight of sucrose is 342 daltons. It should be noted that under vari-
ous conditions in mass spectroscopy the molecular ion peak is not always observed.
However, in the positive ion mode (and often with the addition of a charged ion,
e.g., Na
+
), an M
+
ion (or MH
+
or M+Na) is generated, followed by subsequent
fragmentation, as shown in Figure 5.6. In the example, the glucose fragment is
seen as molecular mass, m/z 180.16 and fructose has a molecular mass, m/z 180.16.
Thus, the fragment ion peaks at m/z 341.1 and 179 come from the intact sucrose and
Peak
#
Frequency
Intensity
Sucrose
[Hz]
[PPM]
1
2
3
4
5
6
7
8
9
10
11
12
10700.879
9542.797
8456.364
7972.468
7724.588
7579.442
7556.326
7425.701
7242.073
6548.308
6453.203
6327.044
106.3573
94.8470
84.0488
79.2393
76.7756
75.3330
75.1032
73.8049
71.9798
65.0844
64.1392
62.8853
14.24
21.82
22.63
16.27
18.90
21.72
22.60
22.62
20.85
18.49
14.09
15.61
3
7
8
2
6
9
5
10
4
12
11
1
HO
11
12
O
7
2
O
O
HO
1
3
10
9
8
5
HO
4
HO
OH
HO
6
OH
OH
220
200
180
160
140
120
100
80
60
40
20
0
ppm
FIGURE 5.5
13
C NMR spectrum of sucrose showing all C signals.
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